This invention relates to a full color image reproduction or recording apparatus which is capable of reproducing full color image with great speed.
In conventional electrophotography or xerography, a photosensitive plate, consisting of photo conductive member placed upon a conductive backing, is uniformly charged and the plate is then exposed to a light image containing original subject matter to be reproduced. Under the influence of the light image, the charge on the photoconductive member is selectively dissipated in the light stuck regions thereby producing latent electrostatic image of the original. The charged latent electrostatic image is then developed by bringing oppositely charged, finely divided electroscopic marking particles called toner into operative communication with the plate in a manner so that the toner particles are attracted into the imaged regions. After development, the visible image is transferred to a final support material, such as paper or the like, and the image affixed thereto to form a permanent record of the original.
The basic electrophotographic process can be adapted to produce full color reproductions by using well known subtractive color printing techniques. It is conventional, in the electrophotographic system, to first color separate the original into the primary color components of red, green and blue. Each component is then used to record a separate latent electrostatic image on the surface of a photoconductive plate and the images are developed with toners containing colorants that are the complements of the primary colors recorded. The recorded red, green and blue color components are developed with toner containing the colorants of cyan, magenta and yellow. Each developed image is individually transferred to a sheet of final support material to create a full color rendition of the original.
Because of inherent limitations found in most known colorants, it is generally necessary to employ costly and complex masking and/or balancing techniques to achive a faithfull color reproduction. Furthermore, because of the number of exposure and transfer operations invloved, registration is also a problem in this type of system. Any disadvantages that might be associated with the subtractive color printing process are certainly offset by the quality of the full color renditions produced.
Hitherto various color reproduction method and apparatus have been proposed and some are actually reduced to commercial products. One of these machines is shown in FIG. 1. Referring to FIG. 1, a conventional multicolor image recording apparatus comprises a platen 32 for mounting a color original 31 thereon, a drive mechanism 33 for reciprocating the platen 32 upon scanning under the original 31 mounted condition, a motor 34 as a drive source of the drive mechanism 33, a scanning unit 35 for projecting light to the original 31 upon scanning and converging reflective light from the original 31 through a filter to a predetermined position, a phtosensitive drum 36 for receiving the light from the scanning unit 35 and forming latent images for cyan, magenta and yellow during three rotations thereof, a charging unit 37 for uniformly charging a surface of the photosensitive drum 36 prior to exposure, developing units 38a, 38b and 38c for developing cyan, magenta and yellow images during three rotations of the drum by adhering toners of each color to the latent images formed on the photosensitive drum 36 to form a visible image, a motor 39 for driving the phtosensitive drum 36, a paper supply cassette 40 for storing many copy papers 60 of required size, a paper feed belt 41 for feeding only one paper from the paper supply cassette 40 at a timing when the visible image reaches a transfer position, a motor 42 for driving the belt 41, a feed roller 43 for feeding the supplied paper to the transfer position, a transferring unit 44 for transferring the visible image from the surface of the photosensitive drum 36 to the paper 60 fed to the transfer position, a fixing unit 45 for fixing a transferred toner image on the copy paper, a cleaner 46 for removing residual toner adhered to the surface to the photosensitive drum 36 after transferring, and a delivery tray 47 for receiving a copied paper 61 after being fixed.
In the above-mentioned arrangement, when the color original 31 is mounted on the platen 32, and copying conditions are set at a consolo (not shown) to press a start button, the motors 34 and 39, charging unit 37, transferring unit 44 and fixing unit 45 are driven. When the motor 34 is rotated, the platen 32 is started to run and lamp in the scanning unit 35 is turned on to form a first latent image through a red filter onto the surface of the photosensitive drum 36 charged by the charging unit 37. Then, the developing unit 38a is selected to carry out developing by adhering cyan toner onto a surface of the latent image, and in turn, the copy paper fed by the paper feed belt 41 is wrapped around a transfer drum of the transferring unit 44 to carry out transferring. After transferring, residual toner on the surface of the drum is removed, and charging is carried out again. At this time, a green filter is inserted in a light path of the scanning unit 35, and the developing unit 38b is selected to carry out developing by adhering magenta toner onto a surface of a latent image. Then, the magenta image is transferred to the copy paper wrapped around the transfer drum with the cyan image registered with the magenta image to form a mixed color image of the two colors. Next, subsequent scanning and exposing are carried out by using a blue filter, and the developing unit 38c is selected to adhere yellow toner onto a surface of a latent image, thereafter to carry out transferring, thus printing a mixed color image of the three colors. Then, the copied paper is separated from the transfer drum and is fed to the fixing unit 45, and after fixing, it is delivered to the delivery tray 47, thus completing full color copying by a one-drum three-color developing device.
The fact that the above-described process entails three sequential light scanning steps to sequentially expose the photoconductive surfaces is obviously disadvantageous from several standpoints. Since the light source must be energized three times for each full color reproduction, the number of copies which can be made from a given light source is reduced as well by a factor of three and the power requirement for each copy is increased by the same factor. The copy output capability is significantly and adversely affected since the exposure time is a rate limiting factor for any given electrophotographic copying system.
In order to improve the above noted problems, an improved color reproduction system is disclosed in U.S. Pat. No. 3,690,756. The important features of this patented invention include the provision of an optical system which uses the light images produced by a single scanning of a color original to simultaneously form color separation images on three different photoconductive areas. The light image formed by scanning the original copy is passed through a focusing lens assembly and is separated by beam splitters into at least three light beams which are color filtered and conducted along optical paths of equal lengths to expose separate photoconductive areas and thereby record the respective color separation images. The essential part of the patented invention is that a single light scanning of the original can be employed to simultaneously produce three or more color separation images on three or more separate photoconductive areas, thus overcoming the difficulties inherent in known reproduction systems which requires a separate light scanning step for each color separation image.
In the former prior art apparatus, however, although registration error or shift due to mechanical deformation or slippage is hardly generated by using a transfer drum supported by a rigid flange, the photosensitive drum must be rotated three times for making full color copy, thereby causing a recording speed to be disadvantageously reduced.
In the latter prior art device, when a belt is used as a feeding means, there occurs expansion and contraction, waving, deviation and slippage, etc. of the belt. Further, when a chain is used as the feeding means, there occurs vibration and expansion, etc. of the chain. As a result, registration shift is apt to be created. Additionally, as a plurality of marking units (combination of photosensitive drums, developing units, charging units and cleaners) are arranged in a line, size of the recording device in the direction becomes large at least times of the number of each marking unit, and accordingly, it is difficult to make the device compact.